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• Both muscular and cutaneous somatosensory input arrives at the cuneate nucleus. • Muscle somatosensory input dose not evoke any low-frequency response from the cuneate nucleus. • Subcortical high-frequency oscillations include both presynaptic and postsynaptic components. To investigate the subcortical somatosensory evoked potentials (SEPs) to electrical stimulation of either muscle or cutaneous afferents. SEPs were recorded in 6 patients suffering from Parkinson's disease (PD) who underwent electrode implantation in the pedunculopontine (PPTg) nucleus area. We compared SEPs recorded from the scalp and from the intracranial electrode contacts to electrical stimuli applied to: 1) median nerve at the wrist, 2) abductor pollicis brevis motor point, and 3) distal phalanx of the thumb. Also the high-frequency oscillations (HFOs) were analysed. After median nerve and pure cutaneous (distant phalanx of the thumb) stimulation, a P1-N1 complex was recorded by the intracranial lead, while the scalp electrodes recorded the short-latency far-field responses (P14 and N18). On the contrary, motor point stimulation did not evoke any low-frequency component in the PPTg traces, nor the N18 potential on the scalp. HFOs were recorded to stimulation of all modalities by the PPTg electrode contacts. Stimulus processing within the cuneate nucleus depends on modality, since only the cutaneous input activates the complex intranuclear network possibly generating the scalp N18 potential. Our results shed light on the subcortical processing of the somatosensory input of different modalities. [ABSTRACT FROM AUTHOR]

Objectives The study aimed to investigate the site of the movement related inhibition of the human dorsal column nuclei. Methods Median nerve somatosensory evoked potentials (SEPs) were recorded from 18 patients suffering from Parkinson’s disease, who underwent electrode implantation in the pedunculopontine (PPTg) nucleus. SEPs were recorded at rest and during active or passive movement of the thumb of the stimulated wrist. Results The PPTg electrode recorded a triphasic potential generated in the cuneate nucleus. The PPTg potential was subtended by 2 high frequency oscillation (HFO) components: (1) an earlier one with 1000 Hz frequency and (2) a later one with 1700 Hz frequency. Both HFO components were reduced by movement. No major difference between the effects of either active or passive movement was found. Discussion PPTg electrode can record SEPs generated in the dorsal column nuclei (DCN). We suggest that the 1000 Hz and 1700 Hz HFO bursts are generated at pre- and post-synaptical level, respectively. Conclusion Movement exerts both pre- and post-synaptic inhibition on dorsal column nuclei. Significance Investigating the effect of movement on the DCN activity by an intracerebral electrode located at the human PPTg level confirms what early studies in animals suggested. [ABSTRACT FROM AUTHOR]

Objectives To investigate the effect of pure passive movement on both cortical and subcortical somatosensory evoked potentials (SEPs). Methods Median nerve SEPs were recorded in 8 patients suffering from Parkinson’s disease (PD) and two patients with essential tremor. PD patients underwent electrode implantation in the subthalamic (STN) nucleus (3 patients) and pedunculopontine (PPTg) nucleus (5 patients), while 2 patients with essential tremor were implanted in the ventral intermediate nucleus (VIM) of the thalamus. In anesthetized patients, SEPs were recorded at rest and during a passive movement of the thumb of the stimulated wrist from the intracranial electrode contacts and from the scalp. Also the high-frequency oscillations (HFOs) were analyzed. Results Amplitudes of both deep and scalp components were decreased during passive movement, but the reduction was higher at cortical than subcortical level. Also the HFOs were reduced by movement. Conclusion The different amount of the movement-related decrease suggests that the cortical SEP gating is not only the result of a subcortical somatosensory volley attenuation, but a further mechanism acting at cortical level should be considered. Significance Our results are important for understanding the physiological mechanism of the sensory–motor interaction during passive movement. [ABSTRACT FROM AUTHOR]

Objective To investigate the generators of the somatosensory evoked potential (SEP) components recorded from the Pedunculopontine Tegmental nucleus (PPTg). Methods Twenty-two patients, suffering from Parkinson’s disease (PD), underwent electrode implantation in the PPTg area for deep brain stimulation (DBS). SEPs were recorded from the DBS electrode contacts to median nerve stimulation. Results SEPs recorded from the PPTg electrode contacts could be classified in 3 types, according to their waveforms. (1) The biphasic potential showed a positive peak (P16) whose latency (16.05 ± 0.61 ms) shifted of 0.18 ± 0.07 ms from the lower to the upper contact of the electrode. (2) The triphasic potential showed an initial positive peak (P15) whose latency (15.4 ± 0.2 ms) did not change across the DBS electrode contacts. (3) In the last SEP configuration (mixed biphasic and triphasic waveform), the positive peak was bifid including both the P15 and P16 potentials. Conclusion While the P16 potential is probably generated by the somatosensory volley travelling along the medial lemniscus, the P15 response represents a far-field potential probably generated at the cuneate nucleus level. Significance Our results show the physiological meaning of the somatosensory responses recorded from the PPTg nucleus area. [ABSTRACT FROM AUTHOR]